1. Field of the Invention
The present invention relates to an ink jet recording head for use in forming an image on a recording medium by jetting fine ink droplets, and a fabrication method therefor.
2. Related Background Art
It is well known to provide a layer excellent in water-repellency (ink-repellency) on the peripheral face of a discharge port, particularly around the discharge port (orifice) as means for retaining the discharge performance safety or improving the performance of an ink jet recording head by a method of applying a fluoropolymer solvent dispersion-liquid such as KP-801 by Shin-Etsu Chemical Co., Ltd. or a method of depositing amorphous alloy thin film.
However, a water-repellent treatment around the discharge port has an intimate relation with the discharge port forming method, and whether it should be performed before or after the discharge port forming process is a key point, because if they do not match consistently, the discharge port precision and the water-repellency around the peripheral face of the discharge port necessary for an ink jet recording head can not be obtained. That is, a conventional example as above mentioned had the following problems in some cases. In the following, the problems associated with the water-repellent treatment on the peripheral face of the discharge port performed before and after the formation of ink liquid channel will be described.
First, when the water-repellent treatment is performed after the formation of the liquid channel, the liquid channel will be also made water-repellent, whether the material is dry sheet-like or liquid, or whether the method is by application or print, or vapor deposition using fluoropolymer or metallic material, so that print deviation may be caused in using the recording head.
That is, in the conventional example with a method in which a photosensitive dry film is pasted on a substrate provided with heat generating elements as the discharge energy generating element and the wirings, and patterned by photolithography technique to form ink liquid channel walls, and then a ceiling plate is bonded thereto, discharge ports are formed by cutting the substrate vertically to a substrate surface at the last step, with its cut surface serving as a discharge port face. With this method, discharge ports themselves are formed by cutting at the same time with the formation of the discharge port face, whereby it is an important consideration how to prevent the water-repellent material entering the liquid channels, and to apply it near the discharge ports, when the water-repellent material is applied subsequently. To this end, the selection of water-repellent material, the adjustment of viscosity, and the development and improvement for the application method will be sought. For example, with a monochrome head (orifice diameter, e.g., o50 .mu.m) having a resolution of 300 dpi (a pitch of 84.7 .mu.m), and a full-color head (orifice diameter, e.g., o20 .mu.m) having a resolution of 400 dpi (a pitch of 63.5 .mu.m), it was only possible to seek the optimal material and method for each head having a different discharge port diameter and pitch, in which the resolution thus obtained did not necessarily satisfy the required quality level 100%, and there was a problem that the fabrication yield was not improved. FIG. 4 is a view showing this situation, illustrating that a water-repellent material 13 has entered each discharge port 7a to 7c, and there is a site 14 on the peripheral face near the discharge port in which the water-repellent material is not applied. That is, 7a is a discharge port which the water-repellent material has entered, 7b is a normal discharge port, and 7c is a port in which water-repellent material layer is lacking on the peripheral face of discharge port. Note that in the figure, 2 is a substrate, 4 is an ink liquid channel wall, 5 is a buffer layer, and 6 is a glass ceiling plate.
FIGS. 5 and 6 illustrates how an ink droplet is discharged through the discharge ports 7a and 7c, respectively. In FIG. 5, the water-repellent material 13 is attached onto the upper portion of the discharge port 7a, so that an ink droplet 34 in this state is discharged more downward than an axial direction (horizontal direction in this figure) of a liquid channel 8. Note that in FIG. 6, 9 is an ink liquid chamber, 10 is an ink supply port, 11 is a discharge port peripheral face, 12 is a water-repellent material layer, 3 is a discharge energy generating element, and 23 is a connection pad.
As shown in FIG. 6, since the water-repellent material layer 12 on the upper portion of the discharge port peripheral face 11 is lacking, the ink 32 is attached to this portion, and an ink droplet 34 is pulled back by the ink 32 and thus discharged more upward than the axial direction of the liquid channel 8, when the ink is discharged through the discharge port.
On the other hand, with a fabrication method of performing the water-repellent treatment before the formation of discharge ports, the discharge ports are formed after the formation of a water-repellent material layer, so that the discharge port face of the water-repellent material layers has reduced adherence to cause the exfoliation or burrs on the water-repellent material layer, leading to undischarge or print deviation, whether the source material forming the water-repellent material layer is a dry sheet-like or liquid, or whether the method relies on the print or the vapor deposition of fluoropolymer or metallic material.
That is, a conventional example 2 as shown in FIG. 7A may rely on a method in which a photosensitive resin is patterned by photolithography technique on a substrate 2 provided with the discharge energy generating elements and the wirings, and then photosensitive resin portion 19 for use as ink liquid channel is formed and covered with a resin so as to wrap around. With this method, in forming discharge ports, the substrate is cut vertically to a substrate face, with its cut surface serving as a discharge face, but as the discharge port itself is not formed yet, the application of water-repellent material and the surface improvement can be readily made. However, when the photosensitive resin portion 19 corresponding to ink liquid channel is removed by a solvent, the water-repellent material layer corresponding to a discharge port peripheral portion must be removed at high precision correspondingly to an edge of the discharge port. FIG. 7B illustrates this situation. When the photosensitive resin portion 19 in the ink liquid channel portion is removed using a solvent of acetone and an utlrasonic cleaner, the water-repellent material layer on the discharge port peripheral face may produce the exfoliation 17 such as a breakage, or burrs 18, thereby causing wetting deviation or undischarge in the discharge port. When a ceiling plate resin and the water-repellent material are poorly bonded, exfoliation as large as a discharge port may be produced by a blade wiping mechanism of the discharge port provided on a printer if the print is repeatedly made by using such a recording head. Note that 20 is a ceiling plate integrally formed of, for example, epoxy resin.
Another example 3, as shown in FIG. 8A is a method in which a water-repellent material layer 12 is formed on a ceiling plate 15 on which an ink liquid chamber 9, ink liquid channels 8, and a discharge port plate 16 are preformed integrally by injection molding, and then the same layer surface is irradiated by an excimer laser corresponding to a liquid channel pattern to form the discharge ports 7d, in which method the discharge ports are already completed at the time of molding, rather than the cutting. This method is superior in that the water-repellent material can be applied to the discharge port formation face before the formation of liquid channels by the excimer laser, and the water-repellent material is prevented from entering the liquid channels, but because of using the abrasion phenomenon of the excimer laser in forming the liquid channels, the water-repellent material layer 12 on the edge portion of the discharge port may be peeled off to form peeling portion 17, or conversely may be left as burrs 18, as shown in FIG. 8A and as with the conventional example 2, whereby it can not be said that the problems have been completely resolved including an orifice forming process, even though the problems associated with the application process of water-repellent material have been eliminated. If such a ceiling plate 15 is overlaid on the substrate 2 to assemble a recording head, an ink droplet will be discharged more downward than an axial direction of liquid channel 8 due to a burr 18, as shown in FIG. 8A. Note that 7d is a discharge port having the water-repellent material protruding as a burr, 7e is a normal discharge port, and 7f is a discharge port having the peripheral water-repellent material layer peeled off.
As above described, when the water-repellent material enters the discharge port, or is left like a burr, the meniscus shape of the ink is uneven, with its position retracting partially into the liquid channel unstably, and causes a bend in the discharge direction as a kind of extraneous matter, giving rise to a problem such as poor print quality or deviation. Also, when the water-repellent material layer is not correctly formed on the periphery cf the discharge port, that improper portion is more easily wetted by the ink than other portions, and as the printing is continued, a problem associated with the print quality such as wetting undischarge or wetting deviation of ink droplets may arise.